Major Classes of Antibiotics Name Examples Spectrum Mode of Action Biological Source Beta-Lactams Penicillins Penicillin, amoxicillin/clavulanate Gram-positive bacteria, gram- Inhibition of cell wall Penicillium notatum, (Clavamox, Augmentin), ampicillin, negative bacteria (synthetic synthesis by interrupting Cephalosporium species, oxacillin,piperacillin, forms) peptidoglycan formation Streptomyces clavuligerus piperacillin/tazobactam (Zosyn), (clavulanate) ticarcillin, ticarcillin/clavulanate (Timentin) Cephalosporins Cephalothin, Ceftazidime, Cefotaxime Gram-positive & gram-negative Inhibition of cell wall Semi-synthetic bacteria synthesis Carbapenems Imipenem, meropenem Gram-positive & gram-negative Inhibition of cell wall Streptomyces cattleya bacteria synthesis Monobactams Aztreonam Gram-positive & gram-negative Inhibition of cell wall Chromobacterium violaceum bacteria synthesis Aminoglycosides Streptomycin, amikacin, gentamicin, Gram-positive & gram-negative Binds to bacterial ribosome Streptomyces griseus kanamycin, tobramycin, neomycin bacteria (esp. Pseudomonas causing misreading of (streptomycin), spp) mRNA resulting in Micromonospora spp inappropriate amino acid (gentamicin) insertion Quinolones Fluoroquinolones Ciprofloxacin, Moxifloxacin, Greatest efficacy against gram Interferes with activity of synthetic Marbofloxacin, Enrofloxacin -negative organisms bacterial DNA gyrase Less effective against gram- positive Glycopeptides Vancomycin, Teicoplanin Gram-positive bacteria (esp Interferes with cell wall Streptomyces orientales Staphylococcus aureus) synthesis by blocking transpeptidation Lincosamides Clindamycin, Lincomycin Gram-positive & gram-negative Blocks protein synthesis by Streptomyces lincolnensis bacteria (esp. Bacteroides spp) binding to bacterial ribosomes Macrolides Erythromycin, clarithromycin, Gram-positive & gram-negative Blocks protein synthesis by Streptomyces erythreus azithromycin bacteria, not enterics binding to bacterial Neisseria, Legionella, ribosomes Mycoplasma Ketolides Telithromycin Gram-positive and some gram- Intefere with protein Semi-synthetic derivative of negative aerobes synthesis by inhibiting erythromycin Oxazolidinones Linezolid Enterococci, streptococci, Bacteriostatic, inhibits synthetic staphylococci protein synthesis Streptogramins Dalfopristin, quinupristin Gram-negative anaerobes & Prevent binding of tRNA at Semi-synthetic streptococci, staphylococci the ribosome, inhibits protein synthesis Sulfonamides & Trimethoprim SMP/TMX Gram-positive & gram-negative Interferes with folate synthetic bacteria, except Pseudomonas production Tetracyclines Tetracycline, doxycycline Gram-positive & gram-negative Bacteriostatic, inhibits Streptomyces spp. bacteria, Rickettsias protein synthesis Nitroimidazole Metranidazole (Flagyl) Binds to DNA Chloramphenicol Chloramphenicol Gram-positive & gram-negative Binds to 50S ribosomal Streptomyces venezuelae bacteria subunit and Interferes with protein synthesis Polypeptides Polymixin, bacitracin Gram-positive & gram-negative Inhibits cell wall production Bacillus polymyxa, Bacillus bacteria subtilis Polyenes Amphotericin, nystatin Fungi Interfere with fungal plasma Streptomyces nodosus, membrane Streptomyces noursei Rifamycins Rifampin Gram-positive & gram-negative Inteferes with bacterial DNA- Streptomyces mediterranei bacteria, dependent RNA polymerase M. tuberculosis .